Plastic materials have various advantages, such as lightness, design flexibility and moldability, despite lower thermal resistance and flame resistance than metals or ceramics, and thus are widely used as industrial materials in a variety of products from daily supplies to industrial fields including automobiles and electric/electronic products.
There are various types of plastic materials from commodity plastics to engineering plastics that are widely used in various fields requiring various functions and performances.
Among these plastic materials, polyphenylene ether has excellent electrical and mechanical properties and high thermal deflection temperature to be used as engineering plastics in various fields.
Polyphenylene ether was developed by General Electric in the U.S.A. and is used in the form of blends with high impact resistance polystyrenes as useful industrial materials, based on excellent thermal resistance thereof. Recently, the polyphenylene ether is used in alloy form, such as a polyamide/polyphenylene ether alloy, obtained by adding a compatibilizer as a third component to a polyamide/polyphenylene ether, followed by reaction extrusion for compatibilization of non-compatible blends through a chemical process.
Particularly, the polyamide/polyphenylene ether can effectively remedy shortcomings of each resin component to exhibit good balance between thermal resistance, impact resistance and chemical resistance, and is thus applied to exterior components of vehicles, such as a wheel cap, a junction box, and the like, and engine compartment components of automobiles.
Recently, there is a need for a plastic material for exterior components which allows on-line electrostatic painting such that electrostatic painting can be simultaneously performed on the plastic material and other metal components. In order to satisfy such a need, a conductive polyamide/polyphenylene ether resin developed by adding conductive fillers such as carbon fibers or carbon black to the polyamide/polyphenylene ether and is applied to automobile fender components.
Development of the conductive polyamide/polyphenylene ether resin allows plastic exterior components to be subjected to electrostatic painting simultaneously with other metal material components, thereby eliminating a need for an additional painting process and thus achieving reduction in production costs.
However, despite good adhesion to urethane paints used in on-line electrostatic painting for automobiles, such a typical conductive polyamide/polyphenylene ether resin exhibits insufficient adhesion to melamine or acrylic paints, thereby limiting the kind of available paint.
Japanese Unexamined Patent Publication No. 2005-281616 (Patent Document 1) discloses a technique for improving paint adhesion by adding a soluble aluminate metal salt to a resin composition comprising a polyamide/polyphenylene ether resin and a compatibilizer. However, this technique does not secure sufficient improvement in adhesion to melamine paints or acrylic paints, despite improvement in adhesion to acrylic urethane paints.
Japanese Patent No. 3,385,774 (Patent Document 2) discloses a technique for improving adhesion to melamine paints and acrylic paints by melting and mixing polyamide, polyphenylene ether, and polyamine resins. However, since the resin composition of this patent is prepared by simultaneously melting and mixing the polyamine, the polyamide, the polyphenylene ether, and a compatibilizer, the polyamine reacts with the compatibilizer instead of the polyamide to reduce the content of the polyphenylene ether-compatibilizer-polyamide copolymer in the resin composition, thereby reducing impact resistance. As a result, the resin composition of this patent is not suitable for automobile fender components.
Therefore, there is a need for development of a polyamide/polyphenylene ether resin composition that has good adhesion to melamine paints and acrylic paints while exhibiting high impact resistance.